Vat dyestuff paste and process for producing the same



Patented Jan. 7, 1936 UNITED STATES PATENT OFFICE VAT DYESTUFF PASTE AND PROCESS F N. Y., assignors to National Aniline & Chemical Company, Inc., New York, N. Y., a corporation of New York No Drawing.

Application May 11, 1932,

Serial No. 610,704

24 Claims. (Cl. 26061) This invention relates to vat dyestuffs and the process of making them. It relates particularly to the production of vat dyes of the anthraquinone and indigoid series in a finely divided form which is particularly adapted for making dyestufi pastes suitable for use in dyeing textile material bythe printing process.

.As is well known, the printing of textile f abrics with vat dyestuffs, and particularly the vat dyestuifs of the types above mentioned, differs from ordinary dyeing with said dyestuffs in that the fabric is dyed only at particular portions, the remaining fabric being left undyed so as to form a design. In general, textile printing is carried out in practice by transferring a so-called printing paste from a metal roll engraved in accordance with the desired design by passing the fabric to be printed into contact with the roll, the engravings of which are filled with the printing paste. Inasmuch as vat dyes are not soluble and do not directly dye the fiber but are required to be reduced to a soluble form, the printing pastes generally contain a reducing agent, such as sodium formaldehyde sulfoxylate, and alkali in addition to water and an adhesive or thickening material (such as gums, various forms of starch, etc.). Frequently, various additional materials, such as glycerin, glycol ethers and the like are also included in the printing paste to assist in the absorption of the color by the fabric. After the cloth has been printedv with the printing paste, it is generally passed through a dryer, which temporarily fixes the printing paste in the dry form upon the fabric, so as to prevent the paste from spreading and spoiling the design. The dried fabric is then-passed through a steam ager, which is maintained under suitable conditions of temperature and moisture to produce reduction of the vat dyestuff on the fabric to the soluble form, which is absorbed by the fibre, and then the fabric is subjected to an oxidation treatment to reconvert thereduced vat dyestuff to the unreduced, insoluble form. The fabric is then subjected to a washing treatment to removeany residual dyestuff and other materials remaining from the fixing process. A In view of the fact that the details of the formulas of printing pastes used by various printers vary with the individual dyestuffs used, with the mixtures of dyestuffs employed to obtain various color combinations, with the other ingredients used for making the printing pastes, and with the materials treated, vat dyestuffs are not ordinarily sold in the form of the finished printing paste but in the form of a so-called dyestufi paste or color paste, which is generally a water suspension of the unreduced vat dyestuif with which sometimes a small amount of a dispersing agent and/or printing assistants such as glycerol, diethylene glycol, an alkylolamine, and the like have been incorporated. The printer can then mix the required amount of the dyestuflf paste with the other necessary ingredients according to the particular formula to be used. In order to facilitate compounding the formulas, the dyestuffs are generally placed upon the market in the form of pastes containing standard concentrations of dyestuffs, as for example, 10 per cent, per cent, and 30 per cent, or higher, pastes.

It will be readily apparent that a satisfactory 20 dyestuif paste should preferably possess, among others, the qualities of being homogeneous, of being readily poured and mixed with the other ingredients, and of uniformly maintaining its condition over relatively long periods of time, so that large supplies of the dyestufi paste may be maintained in stock and portions withdrawn therefrom as needed; and that the dyestufl in the paste should preferably be in a finely divided form and possess such a physical character that strong uniform prints and clear and sharp outlines will be obtained.

Various processes have been heretofore proposed for the production of vat dyestuffs in the form of pastes resulting from filtration of 8115- pensions of the insoluble dyestuffs, but the products heretofore produced have not possessed all of the physical characteristics desirable in a vat dyestuff paste to be used for making printing pastes. Thus, it has been proposed to produce dyestuff pastes of chlorinated indanthrones or of flavanthrone by blowing air through an alkaline solution of the leuco compounds thereof, or oxidizing them in other ways, and filtering of! the resulting precipitate. And it has been proposed to form a solution of flavanthrone in concentrated sulfuric acid and pour it onto a large amount of ice, or to mix the concentrated sulfuric acid solution of the dyestufl with a large quantity of water (10 parts of water per part of so dyestufl in the form of a sulfate, filter off the sulfate of the dyestuif, and then decompose the sulfate with water, and filter off the resulting precipitate. These products are not satisfactory for making printing pastes for one or more of the following reasons: Reduction in the ager does not take place with sumcient rapidity, and the J desired sharpness of outline is not obtained; prints are obtained which are mottled and/0r specked; and, when the paste is mixed with a printing assistant (such as diethylene glycol) and a small amount of a dispersing agent, and the mixture is evaporated to produce a dyestuff paste containing 20 to 45 per cent of dry dyestuflZ-and in some cases even without the addition and evaporationthe paste is so viscous and stiff that it cannot readily be poured and mixed with the other ingredients of the printing paste, or the resulting prints are of inferior tinctorial quality.-

We have discovered that the difficulty had with the vat dyestuif pastes, particularly printing pastes, resulting from the said prior art processes is due mainly to the density, form and size of the particles of dyestuffs in the paste.

We have found, for example, that the size of the particles of the dyestuffs in the pastes of the prior art were either too largeor too small for satisfactory results; thus we have found uneven outlines and slow speed of reduction are caused by particles of too great size, and that the tendency of the pastes, particularly printing pastes, to become stifi' and difiicult to pour is due, at least to a large extent, to the insuificient density and the extremely 'fine subdivision, 1. e., excessively small size of the particles of dyestuff.

It is accordingly an object of our intention to produce pastes of vat dyestuffs containing the vat dyestuffs in the form of particles which are sufliciently small and/or dense to give a welldefined print but which are yet sufllciently large to enable the resulting paste to be readily poured and mixed with other printing ingredients, particularly when in the form of concentrated pastes and/or when containing assistants, such as glycols, their. ethers, etc.

Other bjects of the invention will in part be Obllgfig and will in part appear hereinafter. We ave found, in accordance with the present invention, that the physical form of vat dyestuffs can be controlled, so as to produce vat dyestuif 'pastes highly satisfactory for making printing pastes, by controlling the precipitation of the vat dyestuffs from their sulfuric acid solutions upon dilution with water or other diluting liquid.

' We have found, in accordince with the present invention, by controlling the extent of dilution and the tem erature at which the precipitation is brought ab ut, and preferably also by controlling the speed and order of mixing the solution and the diluting liquid, that the resulting precipitates form dyestuif pastes which have excellent fiuidity and workability, which pad well, and which are especially adapted for making printing pastes of excellent quality.

- The invention accordingly comprises the steps and the relation of one or more with others there-' of which will be exemplified in the process here.

inafter disclosed. and the products having the a sulfuric acid solution of a vat dyestuifis mixed with warm or hot water, and the resulting precipitated dyestuif is separated from the remaining solution. The sulfuric acid solution is preferably added to the water to'efiect rapid dilution.

. The separated precipitate then may be washed with water, to remove the acid, and/or with alkali followed by a water wash, and made into a paste in any suitable manner.

The amount of water employed should be greater than that which would cause considerable separation of the dyestuff in the form of the sulfate, or oxonlum salt, and less than that which would cause considerable separation of the dyestuff in the form of amorphous flocks. Ordinarily the water may be employed'inamounts of about 0.5 to about 2 parts by weight, and preferably 0.7 to 1.5 parts by weight, per part of sulfuric acid solution of-the dyestuff. It is desirable that the sulfuric acid solution and the water he at such temperatures that the temperature of the resulting mixture is not substantially below 50 C., and preferably between 60 C. and the boiling point of the mixture. For best results, the sulfuric acid solution and the diluting water should [both be at a temperature not substantially below 50 C., and the sulfuric acid solution should be rapidly added to the water, preferably without agitation other than that produced by the addition. After the acid solution has been added to the water the mixture should preferably be agitated. If desired the mixture of precipitate and solution produced by the dilution may be further diluted with any suitable amount of water (hot or cold) to facilitate handling and separation, without adversely affecting the quality of the product.

The products thus obtained appear to contain the dyestufl in a very finely divided, non-flocculent form and/or have a density greater than the products obtained by drowning the sulfuric acid solution in a large quantity of water and less than the products ordinarily obtained by the aqueous hydrolysis of the oxonium salt and produce pastes which have superior qualities as to fluidity, padding and printing. In some cases the product appears to be crystalline in form, while in other cases a definite crystalline structure is not apparent; the product appears, however, to tend to the semi-crystalline or crystalline form, as evidenced by the paste having a sheen in reflected light when stirred. In some cases the process produces a modification inthe shade of dyeing obtained with-a particular dyestuif. While the resulting dyestuif may, for that reason, not be suitable for producing dyeings or prints of the usual shade for that dyestuff, it may be used to produce dyeings of the modified shade, and has in addition the advantageous physical properties above set forth.

The process is applicable to the production of dyestufl pastes of various vat dyestuffs. Thus it may be employed to produce pastes of vat dyestuffs of the anthraquinone series, as for example, the indanthrone dyestuifs, the fiavanthrone dyestuffs, the pyranthrone dyestuffs, the benzanthrone dyestuffs (the violanthrones, isoviolanthrones, etc), the naphthacridone dyestuffs, the anthanthrone dyestuffs, (including the iii) ' naphthalenesulfonic chloro-, bromo and other derivatives thereof),

etc.; of vat dyestuffs of the indigoid series, as for example, the halogenated indigo dyestuffs, the

described for example in U. S. P. 1,847,330 or The conditions of temperature, concentration and amount of sulfuric acid, amount of water employed for the dilution, and the like are some- I what interdependent and may vary for optimum results with the different dyestuffs treated. Ordinarily from about to about parts by weight of concentrated sulfuric acid per part of dyestufi may be employed to produce satisfactory results, and the sulfuric acid may vary in strength, prefv erably from about 90 per cent. sulfuric acid to.

oleum'. For ease in operation sulfuric acid mono- I hydrate is preferably employed to dissolve the dyestuif and if desired the solution then may be diluted to a more optimum concentration. The temperature of the sulfuric acid solution preferably should not be raised to such a. high value that, with the strength of sulfuric acid employed, sulfonation will occur toany substantial extent; as otherwise the yield and/or quality of the resulting dyestuff paste will be decreased.

In some cases superior results may be obtained by preliminarily diluting the solution of the vat dyestufi in concentrated sulfuric acid with water, alcohol, acetic acid or a substance containing water of crystallization, so as to reduce the concentration of the sulfuric acid solution to the point of about incipient crystallization or precipitation. but without producing any substantial crystallization or precipitation, of the vat dyestuif from the solution, and then adding the diluted solution to the warm or hot water to produce the final precipitation. In individual cases the desired result may be secured even if a small amount of the vat dyestufi precipitates, or crystallizes in the form of the sulfate, in the preliminary dilution.

The precipitate formed in accordance with the process of the present invention may be separated from the remaining solution ofsulfuric acid in any suitable manner, as for example by centrifugation, vacuum or pressure filtration, etc.; and the resulting separated precipitate (which will hereinafter be referred to as the filter cake) may be made into a dyestuff paste in any suitable manner. .It is preferably agitated with the addition of a small amount (1 to 5 per cent.) of a suitable dispersing agent; as for example a polynuclear aromatic sulfonic acid, an alkyl-, aralkyl-, or cycloalkyl-, polynuclear aromatic sulfonic acid, aldehyde condensation products of any of the said sulfonic acids, a sulfite cellulose waste liquor product, etc. (such as, acids; propyl-, butyl-, benzyl-, or cyclohexyl-naphthalenesulfonic acids; condensation products of formaldehyde with the said naphthalene and substituted naphthalenesulfonic acids; ligninsulfonic acid; mildly oxidized sulfite cellulose waste liquor; etc.).

Thus, for

' the purification of vat dyestuffs.

If it is desired to market the paste ina concentrated form and containing a printing assistant, such as an alkylalomine, 9. glycerol, a glycol, a thioglycol, a polyglyccrol, a polyglycol, or other ether of .glycerine or of glycol, etc., the printing assistant may be incorporated into-the paste, and water may be removed by evaporation tothe desiredextent. The pastes obtained in this manner rem in fluid even in concentrated form, and

maybe eadily mixed with other ingredients.

The process of the present invention may be employed in conjuction with other processes for For example the vat dyestufl may be purified by crystallization in the form of a sulfate, or oxonlum salt, in the well-known manner (for example by the gradual addition of a very small amount of water or .ice to a solution of the vat dyestuff in concen-,

trated sulfuric acid, and filtering off the crystallized sulfate, or oxoniumsalt, thereby produced), and the purified crystals then may be redissolved in concentrated sulfuric acid and subjected to the process of the invention; or the dyestuff (as for example flavanthrone, or halogenated ,di-

benzanthrones or isodibenzanthrones) in the form of an aqueous suspension may be subjected to an oxidation treatment, as for example, with analkali. or alkaline earth metal hypochlorite in the well-known manner, either before or after undergoing precipitation by the process of the present invention, and, if necessary, may then be subjected to the process of the present invention to produce it in the desired form.

The invention will be illustrated by the following specific examples. The parts are by weight. 1

Example 1'.100 lbs. of flavanthrone -(Co1our Index No. 118) is dissolved in 1000 lbs. of sulfuricacid monohydrate at 100 C. The-resulting solution is then cooled to about 50 C. and

poured rapidly into 666 lbs. of water at an initial temperature of 60 to 65 C. without stirring. The resulting mixture isthen thoroughly mixed by agitation. To the agitated mixture, there is added water (at room temperature) in sufficient amount to reduce the concentration of the sulfuric acid to about 10 to per cent. strength, and the precipitated fiavanthrone is filtered off on a nutsch under vacuum and washed with water until it is acid free. drawn ofi from the precipitate on the nutsch; the precipitate is removed and made into an aqueous or printing paste of any desired strength in any well-known manner.

high dye content, on being stirred with a dispersing agent (e. g., 1 to 3 per cent. by weight of Leukanol) becomes fluid and can be readily poured from one container to another. over, such a paste after treatment with a dispersing agent is capable of being mixed with printingassistants and evaporated to give a pas-e which is still fluid even when the dye content of such a paste is to per cent.

The fiavanthrone obtained inthis manner ap pears under the microscope to be in the form of finely sub-divided crystals which are in the shape of small blades or prisms. While crude flavanthrone may be treated in, accordance with this example, purified fiavanthrone is preferably employed. The sulfuric acid may vary considerably in amount and strength so long as it is suflicient to hold the dyestuif in solution under the existing temperature conditions before the When no more water is The press-cake (nutschcake) obtained in this manner. in spite of its Moresolution is mixed with water. As'above pointed out, the temperature also may vary, but a tem-.

perature and concentration of acidwhich will produce substantial sulfonation should preferably be avoided.

Example 2.--100 lbs. of dichloreisoviolanthrone 1 (Colour Index No. 1104) is dissolved in 1000 lbs.

washed acid free with water, then with a dilute to 82 per cent. of water.

soda ash solution, and finally with water until free from alkali. Ordinarily, the press-cake contains about 13 to 18 per cent. of dyestuff and 87 This press-cake upon the addition of a small amount of a dispersing agent (1 to 3 per cent. of Leukanol) becomes fluid and is readily incorporated with printing assistants (glycerol, diethylene glycol, etc.) to give color pastes which can be evaporated to give even stronger pastes which remain fluid. 'Further, these fluid pastes are readily mixed with thickening agents, such as gums, starches, dextrine, etc., to give printing pastes which are also fluid and give prints of full strength which are even in character.

The dichlor-isoviolanthrone obtained in accordance with this example is, in the form of a paste, dark chocolate to reddish brown in color 60 to 90 C. are preferred. If desired, the di-\ lution of the acid solution may be omitted and the undiluted solution may be poured directly into the water to produce precipitation of the dyestuff. In the latter case a sulfuric acid concentration of about 90 per cent. is preferably employed instead of the sulfuric acid monohydrate for preparation of the original solution. The procedure including the dilution isgpreferred, however.

Example 3.Dissolve 350 parts of indanthrone in 5250' parts of well-stirred sulfuric acid of 66 B. strength at 50 C. in a suitable chlorination kettle equipped with cooling means and an agitator and connected with a vent. Into this solution, kept well agitated and maintained at a temperature between 15 and 50 C., and preferably at about 0., pass a current of chlorine, preferably through a diffuser, at a rate slightly in excess of that at which it is approximately absorbed, that is, about 85 to 90 per cent. or more of the chlorine passed in is absorbed. It is preferable that substantially all of the air in the apparatus be displaced by chlorine during the process. When a test sample shows the desired percentage of chlorine to be present, the addition of chlorine is discontinued. The reaction mixture is then treated with 525 parts of crystallized ferrous sulfate, keeping the temperature below C., and stirring for about one-half hour. The temperature of the mixture is then raised to about 125 C. and held at this point for about one hour. The resulting reaction mixture is then drowned as quickly as possible in 8600 nemas parts of water, which has been preheated to 60' 0., without stirring. The diluted mass is then stirred and sufficient cold water-is added to dilute the sulfuric acid to a strength of about-'7 per cent. to 10 per cent. The precipitated product 5 is then filtered off, washed first with water until practically free from acid, then with a 2 per cent.

sodium-carbonate solution, and finally with water until substantially free from alkali. The resulting chlorindanthrone produces printing pastes of 10 very good quality. a

Since changes may be made in carrying out the process and in the products above described without departing from the scope of the invention,'all matter contained in the above descrip- 15 tion is to be interpreted in an illustrative and not in a limiting sense, except as limited appended patent claims.

We claim;

1. A process for producing a vat dyestufl 11120 finely divided, solid form, which comprises mix-.- ing a solution of the vat dyestufl in concentrated sulfuric acid with warm to hot water, the amount of water being greater than that which would cause separation of the dyestufl in the 25 form of the sulfate and less than that which would cause substantial separation of the dyestuff in theform ofamorphous flocks, whereby a precipitate of the vat dyestufl is produced.

2. A process for producing a vat dyestufl in 30 flnely divided, solid'form, which comprises rapidly diluting a solution of the vat dyestuff in concentrated sulfuric acid with warm to hot water, the amount of water being greater than that which would cause separation of the dyestuff in the 5 form of the sulfate and less than that whichwould cause substantial separation of the dyestufl in the form of amorphous flocks, whereby a precipitateof the vat dyestufl is produced.

3. A process for producing a vat dyestuff in finely divided, solid form. which comprises rapidly adding asolution of the vat dyestufl in concentrated sulfuric acid at a temperature not substantially below C. to water which is at a temperature between 50 C. and the boiling point, the amount of water being greater than that which would cause separation of the dyestuif in the form of the sulfate and less than that which would cause substantial separation of the .dyestufl in the form of amorphous flocks, whereby a pre clpitate of the vat dyestuif is produced, and separating the precipitate fromthe remaining liquid.

4. Afprocess for producing a vat dyestufl in by the finely divided, solid'form, which comprises rapidly diluting a solution of the vat dyestuff in concentrated sulfuric acid with about 0.5 to about 2 parts of water which is at a temperature not substantially below 50 0., whereby a precipitate of the vat dyestufl is produced.

5. A process for producing a vat dyestuff in so flnely divided solid form, which comprises adding a solution of the vat dyestufi 'in concentrated sulfuric acid to about 0.7. tolabout 1.5 parts of water which is at a temperature not substantially below 50 0., whereby a precipitate of the vat c5 dyestuif is produced.

6. A process for producing a vat dyestufl in Ufinely divided, solid form, which comprises rapidly adding a solution of the vat dyestuif in concentrated sulfuric acid to about 0.5 to about 2 parts of water, the sulfuric acid solution and the water both being at temperatures not substantially below 50 0., whereby a precipitate of the vat dyestuif is produced, and separating the precipitate from the remaining liquid.

. of a dispersing agent, the improvement which comprises rapidlyqadding a solution of the vat dyestuff in about 5 to 10 times its weight of concentrated sulfuric acid to about 0.5 to about 2 I parts-of water, the sulfuric acid solution and the water both being at temperatures not substantially below 0., whereby a precipitate of the vat dyestufl? is produced, and separating the precipitate from the remaining liquid.

8. The process of making a dyestuif paste of an anthraquinone vat dyestuif which comprises adding a solution of the anthraquinone vat dyestuff in concentrated sulfuric acid to about 0.5 to about 2 parts of water which is at a temperature not substantially below 50 C., whereby a precipitate of the vat dyestufl is produced, and separating the precipitate from the remaining liquid.

9 In the process of making an anthraquinone dyestuif composition in the form of a paste by precipitating the vat dyestuif, separating the precipitate, and stirring the separated precipitate in the presence of a dispersing agent, the improvement which comprises rapidly adding a solution of the anthraquinone vat dyestuff in about 100 per cent. sulfuric acid to about 0.7 'to about 1.5 parts of water, the sulfuric acid solution and the water both being at temperatures not substantially below 50 (7., whereby a precipitate of the vat dyestufi is produced, stirring the resulting mixture, and separating the precipitate from the remaining liquid by filtration.

10. The process of making a vat dyestufi paste which comprises diluting a solution of the vat dyestuif in concentrated sulfuric acid with a diluent selected from the group consisting of water, alcohol, acetic acid and a substance containing water of crystallization, the extent of dilution being insuflicient to cause substantial separation of the dyestuif at 50 C., rapidly adding the diluted solution at a temperature above 50 C. to 0.5 to 1.5 parts of water which is at a temperature not substantially below 50 0.,

whereby a precipitate of the vat dyestufl is produced, and separating the precipitate from the remaining liquid.

11. The process of making a dyestufi paste of an anthraquinone vat dyestuff which comprises diluting a solution of the vat dyestufi in concentrated sulfuric acid with a diluent selected from the group consisting of water, alcohol, acetic acid and ferrous sulfate containing water of crystallization, the extent of dilution being insuflicient to cause substantial separation of the dyestufi at 50 0., rapidly adding the diluted solution at a temperature above 50 C. to about 0.7 to 1.5 parts of water which is at a temperature not substantially below 50 0., whereby a precipitate of the vat dyestuif is produced, and separating the precipitate from the remaining liquid.

12. A process of making a dyestufl' paste of an anthraquinone vat dyestuff selected from the dibenzanthrone and pyranthrone series which comprises diluting a solution of the vat dyestufl? in sulfuric acid monohydrate with a diluent selected from the group consisting of water, alcohol and acetic acid, the extent of dilution being insuflicient to cause substantial separation of the dyestufl at 60 C., rapidly adding the solution at a temperature between 60 and C. to about an equal amount of water which is at a temperature above 60 (3., whereby a precipitate of the aoaaeas vat dyestufl is produced. stirring the resulting mixture, dfluting the resulting mixture with.

water, and filteringoif the precipitate from the tering oil the resulting precipitate.-

14. The process of making a dyestuff paste of a 15 halogenated isoviolanthrone which comprises rapidly pouring a solution of a halogenated isoviolanthrone in 10 parts of concentrated sulfuric acid at a temperature of 60 to 90C. into a substantially equal weight of water at 65 to 75 0., 2'0 stirring the mixture after the addition has been completed, and filtering off the precipitate.

15. In the process of making a halogenated isoviolanthrone in the form of a paste by precipitating the halogenated isoviolanthrone, separat- 2. ing the precipitate, and stirring the separated precipitate in the presence of a small amount of a dispersing agent, the improvement which comprises diluting a solution of a halogenated isoviolanthrone in 10 parts of sulfuric acid mono- 30 hydrate with about 1.7 parts of water, rapidly mining the resulting solution at a temperature of 60 to 90 G. into about 10 parts of water at 65 to 75 C., stirring the mixture after theaddition has been completed, further diluting the resulting suspension, and filtering off the precipitate.

I6. A vat dyestufi free from a chlorindanthrone nucleus in a non-fiocculent, finely-divided form obtainable by the processof claim 1.

17. In a vat dyestuif composition adapted to be mixed with a dispersing agent and/or other material for the production of a dyestuff paste or a printing paste, a vat dyestufi free from a chlorindanthrone nucleus in a non-flocculent, finely divided form obtainable by the process of claim 3.

18. As a new composition of matter, an aqueous suspension of an anthraquinone vatdyestufl free from a chlorindanthrone nucleus in a nonflocculent, finely divided form, the dyestufi particles being substantially the size of those obtainable by the process of claim 6.

19. An anthraquinone vat dyestufi free from a chlorindanthrone nucleus in a non-fiocculent, 5 finely divided form obtainable by the process of claim 8.

20. Asa vat dyestufi paste, an aqueous suspension of an anthraquinone vat dyestufi selected from the benzanthrone and pyranthrone series in a non-fiocculent, finely divided form obtainable by the process of claim 12.

21. As a vat dyestufi paste, an aqueous suspension of a fiavanthrone vatdye'stufi in a non-flocculent, finely crystalline form obtainable by the process of claim 13.

. 22. In the process of producing a pigment by dissolving a vat dyestufi in sulfuric acid and drowning the mass in water, the improvement which comprises using substantially boiling water as the drowning medium.

23. A process for producing an indanthrone dvestufi in finely divided solid form, which comprises treating said dyestuff with a sufiicient quantity of concentrated sulfuric acid to com- 75 massinto a volume of water sumcient to reduce the ultimate concentration of the acid to less than 50 per cent by weight, the water being' maintained during' this procedure at a temperature substantially near its boiling point.

.24. A process torproducing a vat dyestui! in finely divided solid. form, which comprises mixing a solutionoi the vat dyestufl in concentrated sulfuric acid with between about 0.5 and about 2 parts of warm to hot water for each part of suliuric acid solution.

' MAURICE H. FLEYSHER. JAMES OGILVIE. 

